Conventionally, valves that are used, in particular, in semiconductor manufacturing apparatuses have been required to be compact and capable of high-speed opening and closing. In order to meet such requirement, for example, solenoid valves including a solenoid with a reduced size, as shown in FIG. 5 to FIG. 7, have been proposed (Patent Document 1).
FIG. 5 is a longitudinal cross-sectional view showing a solenoid valve of normally closed type, and FIG. 7 is a longitudinal cross-sectional view showing a solenoid valve of normally open type. FIG. 6 is a cross-sectional view showing, in enlargement, the solenoid portion of the solenoid valve shown in FIG. 5. A metallic diaphragm 5 is provided above a valve seat 2 formed on the bottom face of a valve chest 1a. The peripheral edge of the metallic diaphragm 5 is held sandwiched between a bonnet 3 inserted into the valve chest 1a and a valve body 1 in an airtight manner. A stem 7 is actuated using an electromagnet M fixed to the valve body 1, and the metallic diaphragm 5 is seated or unseated on or from the valve seat 2 against the elastic reaction force (about 17 kgf) of a spring 8. The electromagnet M has a tubular plunger 19, a tubular yoke 18 surrounding the plunger 19, a coil 17 provided inside the yoke 18, and a movable iron core 20 that is provided facing an end face of the yoke 18 with a gap G in between and that is screwed to the plunger 19.
The yoke 18 is formed as a double cylinder made up of a short first yoke portion 18c located on the inner side and a tall second yoke portion 18d located on the outer side. The coil 17 is provided between the first yoke portion 18c and the second yoke portion 18d. An end of the coil 17 on the movable iron core side is located near an end face 18d′ of the tall second yoke portion 18d on the movable iron core side. The movable iron core 20 is formed of a tubular first movable iron core portion 20c having a wall thickness that is the same as the thickness of the first yoke portion 18c and a flange-shaped second movable iron core portion 20d. The end face 18c′ of the first yoke portion 18c and the end face 20c′ of the first movable iron core portion 20c, as well as the end face 18d′ of the second yoke portion 18d and the end face 20d′ of the second movable iron core portion 20d faced one another such that there is a gap G of about 0.4 mm therebetween and that the gap G between the end face 18c′ of the first yoke portion 18c and the end face 20c′ of the first movable iron core portion 20c is located closer to the first yoke portion 18c by a distance S from the movable iron core-side end of the coil 17 even when the electromagnet M is not in operation. A shaft 21 coupled to the stem 7 and the plunger 19 are coupled together by means of an adjust screw 15. The adjust screw 15 enables fine adjustment of the gap G between the yoke 18 and the movable iron core 20 fixed to the plunger 19.
The actuator body 9 is formed of aluminum in a cylinder shape, is fixed to the upper end of the bonnet 3 by a fixing nut 13, and is prevented from rotating using a set screw 14. A solenoid base 12 is fixed by being screwed in the upper portion inside the actuator body 9, and the electromagnet M made up of the coil 17, the yoke 18, the plunger 19, the movable iron core 20, and so forth is fixed to the solenoid base 12 by a set screw 16. The upper portion of the actuator body 9 is sealed by an actuator cap 10 made of aluminum, and a lead wire 22 for supplying an excitation current is guided to the outside through a lead protector 23 provided at the cap 10.
For the solenoid valve 30A shown in FIG. 5, when the coil 17 is de-energized, a disc 6 presses against the metallic diaphragm 5 by the spring 8 depressing the flange portion of the stem 7, and the metallic diaphragm 5 is caused to be seated on the valve seat 2 against its elasticity, and thereby a flow passage 1b is closed. At this time, the movable iron core 20 coupled via the stem 7, the shaft 21, and the plunger 19 is also pulled down by an amount corresponding to the solenoid stroke gap G. Upon energizing the coil 17, the movable iron core 20 is lifted up by an amount corresponding to the solenoid stroke gap G against the elastic force of the spring 8 (about 17 kgf), so that the shaft 21 threadedly coupled via the movable iron core 20 and the plunger 19 is pulled up, and by pulling up the stem 7 integrated with the shaft 21 and the disc 6 fixed to the stem 7, the metallic diaphragm 5 curves upward by its elasticity so as to move away from the valve seat 2, causing the flow passage 1b to open. Note that a solenoid valve 30B as shown in FIG. 7 is a solenoid valve obtained by changing the solenoid valve 30A in FIG. 5 in design into a normally open type.
For these solenoid valves, it is necessary to control the current so that the valves are opened or closed by instantaneously passing a relatively large current through the coil upon starting the fast opening or closing operation to attract the movable iron core 20 and lift it up by an amount corresponding to the gap G, and, after the movable iron core 20 has been attracted, the open or close state of the valves is maintained by passing a relatively small current necessary for holding the movable iron core 20 in the attracted state. For this reason, as shown in FIG. 8, the actuation of the solenoid valve 30A (B) is controlled by connecting a large-capacity, high-voltage aluminum electrolytic capacitor and a dedicated power source 50 including a charge/discharge control circuit for the capacitor to the solenoid valve 30A (B) via a cable 51.
FIG. 9 is a block diagram showing the circuit configuration of a conventional dedicated power source, and FIG. 10 is a timing diagram showing the output waveform of the dedicated power source in a solenoid valve of normally closed type. In FIG. 9, reference numeral 52 denotes an input terminal that receives a supplied power of AC 100 V to 240 V, 53 denotes an AC/DC converter, 53a denotes a high-voltage line of DC 48 V, 53b denotes a low-voltage line of DC 3 V, 54 denotes an electrolytic capacitor with a rated voltage of 100 V and a capacitance of 4700 μF, 55 denotes a switching circuit, 56 denotes a timing circuit that switches the switching circuit 55, 57 denotes a common line, and 58 denotes an input terminal for opening or closing signals.
A solenoid 32 has a diameter of 23.6 mm and a height of 25 mm, with a weight of 70 g, the ferromagnetic material such as the movable iron core is made of 35 wt % of cobalt and 65 wt % of iron, the number of turns in the coil 17 is 315, and the resistance value of the coil 17 is 5.6Ω (20° C.). The solenoid 32 exerts an attraction force of 25 kgf at about 5.0 A when the gap G is 0.4 mm, and exerts an attraction force of about 25 kgf at 0.4 A when the gap G is 0 (when attracting).
When an opening or closing signal indicating ON (valve open) is input to the dedicated power source, the timing circuit 56 connects the switching circuit 55 to the line 53a to pass a drive current having a relatively large current value (about 4.8 A) through the solenoid 32, thus opening the closed valve. After a certain time period (e.g., about 5 ms), the timing circuit 56 switches the switching circuit 55 from the line 53a to the line 53b to pass a drive current having a relatively small current value (e.g., 0.4 to 0.55 A) through the solenoid 32 in order to maintain the open state of the valve. Patent document 1: JP 2000-240838 A